Cut your de-cored pineapple slices in half. Place them on the arch of the slice with the cut ends facing up. Then put a Maraschino cherry next to it and add another pineapple slice. Keep going until the whole cake pan has a layer of pineapples and cherries.
In a separate mixing bowl, combine yellow cake mix with vanilla pudding mix. Then pour in some pineapple juice, milk, and vegetable oil. Crack three eggs into it and stir thoroughly.
Pour the batter into the Bundt pan on top of the pineapple slices. Even it out with a spatula.
Then pop your pineapple upside down Bundt cake into the 350°F oven for 30 minutes.